9 Orber Examples

9.1 A Tutorial on How to Create a Simple Service

Interface Design

This example uses a very simple stack server. The specification contains two interfaces: the first is the Stack itself and the other is the StackFactory which is used to create new stacks. The specification is in the file stack.idl.

Generating Erlang Code

Run the IDL compiler on this file by calling the ic:gen/1 function

\0111> ic:gen("stack").

This will produce the client stub and server skeleton. Among other files a stack API module named StackModule_Stack.erl will be produced. This will produce among other files a stack API module called StackModule_Stack.erl which contains the client stub and the server skeleton.

Implementation of Interface

After generating the API stubs and the server skeletons it is time to implement the servers and if no special options are sent to the IDL compiler the file name should be <global interface name>_impl.erl, in our case StackModule_Stack_impl.erl.

We also have the factory interface which is used to create new stacks and that implementation is in the file StackModule_StackFactory_impl.erl.

To start the factory server one executes the function StackModule_StackFactory:oe_create/0 which in this example is done in the module stack_factory.erl where the started service is also registered in the name service.

Writing a Client in Erlang

At last we will write a client to access our service.

Writing a Client in Java

To write a Java client for Orber you must have another ORB that uses IIOP for client-server communication and supports a Java language mapping. It must also have support for IDL:CosNaming/NamingContext or IDL:CosNaming/NamingContextExt. If the client ORB support Interoperable Naming Service the Java Client can look like:

Note

If an ORB does not support CosNaming at all the cos_naming.idl file must be compiled and imported.

Building the Example

To build the example for access from a Java client you need a Java enabled ORB (e.g. JavaIDL). The example below is based on JDK-1.4.

fingolfin 127> erl            
Erlang (BEAM) emulator version 5.5.4.3 [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.5.4.3  (abort with ^G)
1> ic:gen(stack).
Erlang IDL compiler version 4.2.12
ok
2> make:all().
Recompile: StackModule_EmptyStack
Recompile: StackModule_Stack
Recompile: StackModule_StackFactory
Recompile: StackModule_StackFactory_impl
Recompile: StackModule_Stack_impl
Recompile: oe_stack
Recompile: stack_client
Recompile: stack_factory
up_to_date
3> 
BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
       (v)ersion (k)ill (D)b-tables (d)istribution
a
fingolfin 128> idlj stack.idl
fingolfin 129> javac StackModule/*.java
fingolfin 130> javac *.java
fingolfin 131> cp StackClient.class StackModule/

How to Run Everything

Below is a short transcript on how to run Orber.


fingolfin 143> erl 
Erlang (BEAM) emulator version 5.5.4.3 [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.5.4.3  (abort with ^G)
1> orber:jump_start([{interceptors, {native, [orber_iiop_tracer_silent]}}]).
ok
2> oe_stack:oe_register().     
ok
3> stack_factory:start().
ok
4> stack_client:run().
1
1
7
4
ok
5>

Before testing the Java part of this example generate and compile Java classes for orber/examples/stack.idl as seen in the build example. To run the Java client use the following command:


fingolfin 38> java StackModule.StackClient "corbaname::localhost:4001#StackFactory"
1
1
7
4
Empty stack
fingolfin 39>